A retractor is a standard component of a seat belt restraint system which includes a spindle receiving the webbing material of the seat belt. The spindle is used to wind up and store the webbing. Generally, the spindle is locked in place upon detection at a potential accident situation in order to restrain the occupant via the seat belt. Recently, retractors have been designed having one or more force limiting elements which are structured to allow the spindle to rotate and pay out the webbing material of the seat belt upon reaching predetermined force levels between the occupant and seat belt. In this manner, the restraint force imposed on the occupant can be limited in a controlled manner, providing a certain load limitation characteristics.
More recent enhancements in load limiters have been directed to addressing the differences in restraining forces required to safely bring occupants to rest. For example, higher restraining forces may be initially applied, followed by lower restraining forces at a later point during an emergency event. To this end, multi-stage load limiting devices have been developed. A multi-stage torsion bar, for example, is such a device. The multi-stage torsion bar is essentially two torsion bars that are axially aligned and joined at respective ends. The appropriate stage or portion of the torsion bar may be selectively activated to provide a secondary load limiting characteristic as desired.